Metallic element



mama'- L. W. MOKEEHAN METALLIC ELEMENT Filed April 11; 1927' Patented Dec. 3, 1929 UNITED s'rATss PATENT OFFICE LOUIS 'W. MOKEEEAN, KALPIIEWOOD, NEW JERSEY, ASSIGNOR '10 BELL TELEPHONE LABORATORIES, INCORPORATED, ,OF NEW YORK, N. Y.,

YORK

Application flledApril 11,

element comprises essentially a single large crystal of iron. This embodiment of the in-.

vention which is described in detail below,

may be regarded as being typical of other embodiments which include elements formed of iron alloys, cobalt, cobalt alloys and other polymorphic metals, that is, metals having a different crystal structure above than below a temperature known as the transformation temperature.

The method of producing such elements in accordance withthis invention comprises establishing a steep temperature gradient in the metal over a range within which lies the transformation temperature, and causing the region of steep temperature gradient to move through the metal at a rate, equal to or less than the rate of crystal growth. If the rate at which the region at the transformation temperature moves through the metal is too great the transformation. may not be completed and the crystal structure appropriate to higher temperatures may be in partjpreserved at low temperatures.

The advantages which are gainedby employing in magnetic circuits monocrystalline iron in place of ordinary iron having a olycrystalline structure are due to the relatlvely j high permeability of the former over awide range of magnetizing forces. and "its lower hysteresis loss. An allo composed of apnickzl and 21 iron suitably heat treated as disclosed-in Patent No. 1,586,884, granted to G. W. Elmen, June Y 1, 1926 has higher permeability and lower hysteresis than ordinary iron at low values of magnetizingforce. The .monocrystalline iron made in. accordance with thisinvention, while not'so good in these respects as this alloy, has the advantage thereover of having high permeability and low hysteresis loss compared with polycr stalline iron at relatively high values 0 magnetic induction.

.6. CORPORATION OI NEW METALLIC ELEMENT 1927. Serial No. 182,973.

The monocrystalline iron and polycrystalline iron saturate at about the same value of induction which is considerably higher than the induction at which the nickel-iron alloy saturates. The mechanical properties of monocrystalline metals also differ substantially from those of ordinary metals having a polycrystalline structure. Although a monocrystalline metal is mechanically weaker than a polycrystalline metal, it is not so subject to defects of elasticity commonly called elastic after-effects and fatigue. The substitution of monocrystalline for polycrystalline iron or other metal is, therefore, sometimes of advantage in places where magnetic properties are not important. y

Metals as ordinarily prepared consist of a large number of small crystals, from about 100,000 to several million in a cubic inch.

This results from the fact that under ordinary conditions when the metal freezes, or when it passes through a temperature transformation, crystallization takes place at a large numberof centers and these crystals grow until they meet one another.

The process of producing large crystals in accordancewith this invention avoids diificulties heretofore encountered and is sufii- The invention may be readily understood by referring to the following detailed description' in connection with the accompanying drawing in which,

Fig. 1 is a diagrammatic view of an apparatus which is suitable for producing large crystals inaccordance withthis invention;

Fig. 2 is a diagrammatic view ofa rela a large portion of the magnetic circuit of which consists of iron in the term of a single large crystal;

. 1' in the rod and the rate at which the Fig. 3 shows for comparison magnetization curves for samples ofmonocrystalhne and -polycrystalline iron, otherwise alike;

Fig. 4 shows permeability curves for the samples of'iron' employed in obtalning the curves of Fig. 3; an

Fig. 5 shows hysteresis loops for the samples of iron employed in obtaining the about 1400 C. As t e iron rod passes out therollers 12 whic furnace temperature is maintained sufficiently high to heat a part ofthe rod to a temperature higher than the transformation temperature (approximately 900 C.) at or just below which will grow iron crystals of the'body-centered cubic form stable at room temperature, a preferred tempera turefor thehottest' art of the rod being of thefurnace, it is. cooled by conduction to I the rollers 16 and by a stream of hydrogen or other suitablegas which flows in through so the opening 14, then through the furnace 11,

"and out through the opemng 15. There is thus established in the iron rod as it passes out-of the, furnace 11 asteep temperature widely separated in the longitudinal direc- "gradient which includes the temperature for owing 'ironcrystals referred to above.-

is means that two points in the rod .not

.tion'may'have respectively atemperature as high as 1400- O. and a 'temperatureas Iow "as, 100 G. or 200 .0. .Only a very small 1 portion of the rod measuredin the direc- 2 tion' of its length is, therefore, at the opti mum crystal-growing temperature of about 900 C. at a given time. The rod is passed through. the oven at a rate e ual to or less than" therate at which the. Ody-centered cubic iron c stals Beenflefin'ite yesta' lished but good results 1 have been obtained by employing 'arate I "although it is possiblethat rateshigher ow. This rate has not equal to 200 centimeters'perhour and less than- "thisvalue are racticable. -It is ap-.

. 'f parent that, when t 'e F steep temperature gradient ust mentioned is maintained paratus. The hydrogen portion" of the rod helps to prevent the oxi-' rod passes. through this region of steep temperature j gradlent is equal to or lessthan .the rate of crystal growth, the rod will have the form of asingle crystal when it passes out of the heatingearild cooling apsi es cooling a ation thereof and to aid in removing carbon. which always increases, hysteresis in magnetic material.

nection with Fig. 1.

After the rod passes through the rollers 16, it may be cut into lengths suitable for use in magnetic circuits such as that of the relay shown in Fig. 2. In this relay the core 17 on which the winding 21 is positioned comprises essentially a single iron crystal of the body-centered cubic form such as obtained by the process described in con- The magnetic circuit is completed through the return magnetic path 18 and the armature 19. The use of monocrystalline iron or other'magnetic materials in the monocrystalline form is advantageous not only in the magnetic circuits of relays, but also in other devices in which high permeability and low hysteresis loss'are desired and which are to be operated at magnetic inductions nearly up to the saturation point of iron, this point heingabout the same for both the single crystal and the polycr stalline iron.

The magnetic c aracteristics of samples of monocrystalline iron and polycrystalline iron are shown respectively by the curves (2 and b of Figs. 3, 4 and 5, these curves being plotted in c. g. s. units. The two samples compared were of the same chemical composition and were treated as nearly as possible in the same way consistently with obtaining the di-iference in crystal size.

The curves of Fig. 3 indicate that both the of H=' 3.75.

Fig. 4shows thatthe permeability of monocrystalline iron (curve a) is high compared with that of the polycrystalline iron (curve b) over a range of magnetizing forces. The monocrystalline iron has an initial permeability of approximately 2000 and a .maximum permeability of about 26000. :Moreover, the permeability of this material is appreciably higher than that of .the polycrystalline iron for values of H from zero to a value well above 1.0 gauss,

the permeability for H=1.0 gauss being 13000 compared with a permeability of about 2000 for the polycrystalline iron.

Fig. 5 shows hysteresis loops for the two types of iron. It is apparent that the area of the hysteresis loop for the monocrystalline iron (curve a) is considerably less than that, of the polycrystalline iron (curve 6) While the process described above for making the monocrystalline metal employs an electric furnace, it is apparent that other methods of obtaining a high temperature gradient in the metal may be employed. For example, electrical current may be passed amass? through the rod'itself by providing'it at suitable points along its length with sliding or rolling electrical contacts to which a source temperature, pieces of'metal having. other a material the structure of which changes formsof cross section or having irregularities in cross section may betreated in accordance with this invention bysuitably vary a ing the shape of the furnace, the tem 'erature metal is propelled through it.

What is claimed'is:

.' 1. 'A process for growing large'crystals in from one type of crystal to another at av temperature Well .below its melting point, which process comprises establishing a steep temperature gradient in the material such that .at a certain position within the region of said temperature gradient the material is at a temperature at which said change in crystal structure occurs, and causing the region of steep temperature gradient .tomove through thematerial at a rate not greater than the rate of growth of the crystals which are stable below said temperature.

2, A process for producing a metallic elemerit a large portion of which is in the form of a single crystal, which'process comprises establishing a steep temperature gradient in a magnetic material having a polymorphic transformation such that at a certain position within the re ion .of said temperature gradient the material isat a temperature at which the crystal structure changes from one type of crystal into another, and causing the region of steep temperature gradient to move through the material at a rate not greater. than the rate of growth of crystals which are stable below said temperature.

3. A process for producing a magnetic element in a material having allotropic modifications andcomprising a single crystal from a metallic blank formed of numerous small crystals, which process comprises progressively subjecting small portions of said metallicblank first to a temperature below the melting point of the metal and well above the temperature at which said single crystal is formed and then to a temperature which said single crystal isformed, and cans ing-a non-oxi izing atmosphere tocome in contact-withjfirst the cooled portion and then the heated portion of said metallic blank.

5. A; process for producing a ma etic element com rising a single crysta from a polycrysta inemetallic-blank which process comprises progressive] subjecting small portions of said metallic b ank first to a tem ratu're'below the melting point of the meta and well above'the temperature at which said single I crystal is formed and then to a temperature well below the tem erature at which said single crystal is forme and passinghydrogen about said blank from the cooled region toward the heated region.

. j 6. A process for producing-an iron element com rising a single' magnetic crystal from an ron blank comprising numerous small crystals, which process comprises passing the blank through a high temperature region and a low temperature region, respectively, at a rate. not greater than the rate of growth of an iron crystal of the body centered cubic form, the portion of the blank in said high temperature region being subjected to a temperature well above 900 C. while the portion of the blank in said low temperature region is subjected to a temperature well below 900 C-- v 7. A process for producing an iron element comprising a single magnetic crystal from an iron blank comprising numerous small crystals, which process comprises passing the blank through a high temperature region and a low temperature region respectively, at a rate equal to or less than the rate of growth of iron crystals of the body centered cubic form, the portion of the blank in said high temperature region bein subjected to a temperature well above 900 while the portion of the blank in said low temperature gion for cooling the blank and for preventing 7 its oxidation respectively.

8. A process for producing an iron element comprising a single magnetic crystal from an iron blank comprising numerous small crystals, which process com rises providing a high temperature region or raising the temperature of a mately 1400 and a low temperature region for cooling a portion of the blank adjacent to said heated portion to a temperature well below 900 (7., and passing said blank through said high temperature and low temperature regions in order respectively at a rate not greater than the rate at which body centered iron crystals are formed.

9. A process for producing an iron element comprising a large magnetic crystal from an iron blank comprising numerous small crystals, which process com rises providing a high temperature region or raislng the temperatnre of a portion of the blank to approximatel 1400 C. and a low temperature region or cooling a portion of the blank adjacent to said heated ortion to a temperature well below 900 5., passing said blank through said high temperature and low tem- 'perature regions in order respectively at a 10 rate not greater than'the rate at which body centered iron crystals grow, and passing a stream of hydrogen about said iron blank from said'ilow temperature region toward V said high temperature :region. a 5 10. The method of-growing large crystals in aimaterial that has a polymorphic change ;in crystal structure below its fusing point, which comprises heating one region of the 1 material to a temperature above the optimum 20 temperature for growth of'erystals stable. at room temperature,'cooling it well below said optimumtemperature at a veryelosely-adja f cent region whereby a narrow region of steep and falling temperature'grad'lent occurs, and 25 causing said materialto f'movecontinuously I ina direction'irom the heated region toward the cooled region at such a. rate that in the regionof'steep falling temperature gradient g a continuous recrystallization occurs." f 30. In witness whereof, I hereunto subscrlbe t name this 11th day of April A. D., 1927.

; I LOUIS W; MQKEEHAN. 

